1. Field of the Invention
The present invention relates, in general, to a process for preparing an industrial polyester multifilament yarn, and in particular, to a process for preparing an industrial polyester multifilament yarn with high modulus and low shrinkage useful as fiber reinforcements of tires. A treated cord produced from the polyester multifilament yarn has an excellent dimensional stability, i.e. high modulus and low shrinkage, and a high tenacity.
2. Description of the Prior Art
Fundamentally applied for the preparation of industrial high modulus/low shrinkage polyester multifilament yarns at high spinning speeds, a multi-stage spin draw process is generally conducted above the glass transition temperature (about 80° C.) and preferably at 110° C. or higher.
According to Japanese Patent Publication No. Hei. 5-32491 by Isoo Saito et al., a drawing temperature is 120° C., and U.S. Pat. No. 4,349,501 by Maxwell C. Hamlyn et al. and U.S. Pat. No. 4,851,172 by Hugh H. Rowan et al. disclose a draw point localizing method with the use of steam at 300° C. or higher.
Furthermore, Japanese Patent Laid-Open Publication No. Hei. 7-70819 by Masayasu Nagao et al. discloses a multi-phase drawing method, in which undrawn yarns with an intrinsic viscosity of 0.85 or more and a density of 1.365 g/cm3 or more are produced by winding yarns at 2500 to 6000 m/min, then undrawn yarns are drawn through multiple stages at 100° C. or lower. However, an object of this invention is to provide a polyester yarn with high modulus and low shrinkage, in which the modulus and the shrinkage of the polyester yarn are similar to those of rayon or vinylon, and so this invention cannot be applied to tire cords requiring high strength.
Particularly, undrawn yarns with a density of above 1.365 g/cm3 have such a high orientation and crystallinity that undrawn yarns can hardly be mechanically drawn, therefore, high strength yarns of above 7.2 g/d required to manufacture tire cords are very difficult to produce.
And Japanese Patent Laid-Open Publication No. Hei. 7-70819, undrawn yarns are drawn at 100° C. or lower through multiple-stages after passing a pre-draw stage.